The present invention relates to a method for the controlled withdrawal of a countersinking electrode in an electroerosion machine, in which in the case of a short-circuit, the countersinking electrode is moved back by a predetermined path length along the previously covered path from the short-circuit point to an intermediate point and in which the countersinking electrode on the predetermined withdrawal path is moved away from the intermediate point if a short-circuit is still present when the latter is reached.
A method for the controlled withdrawal of a countersinking electrode in an electroerosion machine is known from German Patent No. 35 25 683. Thus, if a short-circuit occurs, the countersinking electrode initially moves back along the already eroded path by a predetermined, short distance.
If the short-circuit still has not been removed at the end of this first withdrawal path, then the electrode is moved further away from the short-circuit point over a second, linear path. The latter is described by a withdrawal vector, which has a flexible direction and which is subject to the requirement of removing the electrode as quickly as possible from the short-circuit point.
Particularly in the case of long, eroded paths of limited width, such as e.g. for producing sealing or packing rings, the variable withdrawal vector has the disadvantage that its angle with respect to the side wall becomes increasingly small as a function of the already eroded path length. Therefore the countersinking electrode withdrawal can only take place in a "dragging" manner. This means that the short-circuit is either not removed or is only very slowly removed.
DE-OS No. 37 05 475 discloses an electrode return control system for an electric arc device, in which if a short-circuit state occurs, an electrode is moved away from a position in a workpiece along a path covered by the electrode for working. This publication also discloses a system, in which an object point to which the electrode is directly moved after the occurrence of the short-circuit state is advanced as the working progresses. This means that the deeper the electrode erodes into the workpiece, the deeper the point on the workpiece axis at which the withdrawal movement of the electrode takes place.
As a result of the planetary eroding movement of the countersinking electrode, in principle a path is only widened, so that in this way the countersinking electrode does not directly produce the desired path.
It is also particularly disadvantageous that when a short-circuit occurs, the electrode has produced such an abrasion in the workpiece that, due to the rounding of the electrode, a correspondingly shaped rounding is cut into the workpiece. Thus, a small edge is formed in the workpiece and is damaged on withdrawing the countersinking electrode.